SPT (Standard Penetration Test) in Liverpool

We recently supervised ground investigation for a six-storey residential block on the former docklands near the Leeds-Liverpool Canal. The made ground there, up to 4 m thick over laminated silty clays of the Tarporley Siltstone Formation, demanded reliable strength profiles at depth. That is precisely where the Standard Penetration Test (SPT) proved indispensable. By driving a split‑spoon sampler under controlled energy, we recovered disturbed samples while logging blow counts (N‑values) every metre. The data fed directly into bearing capacity calculations and settlement estimates for the piled foundation. Before mobilising the rig, we always cross‑reference with a calicatas exploratorias to validate the shallow stratigraphy, especially where historical fill may conceal obstructions. In Liverpool, where glacial till and alluvial deposits alternate unpredictably, SPT remains our primary tool for profiling strength variation with depth.

In Liverpool’s mixed glacial and made ground, SPT blow counts provide the essential stiffness profile that direct push methods cannot match.

Process overview

Liverpool’s urban expansion since the Victorian era has reshaped its natural topography. Much of the city centre and waterfront sit on reclaimed land or deep fills from the industrial period. The underlying geology – mostly Triassic Sherwood Sandstone overlain by glaciofluvial sands and clays – creates sharp lateral transitions that a single borehole alone may miss. Running SPTs at 1.5 m intervals through these layers captures the stiffness contrast between the fill, the weathered sandstone zone, and the competent rockhead. We supplement these profiles with ensayo CPT when continuous cone resistance data are needed for liquefaction screening, but the SPT’s ability to retrieve a physical sample for visual classification gives it an edge in heterogeneous ground. The test follows BS EN ISO 22476-3‑18 procedure; we record hammer efficiency on site to normalise N‑values to a 60 % energy ratio, ensuring consistency with the NCEER correlation charts for sand and gravel.

Local context

With an estimated population of over 490,000 and much of the central area built on soft alluvium or uncompacted fill, Liverpool presents a distinct geotechnical risk: non‑uniform settlement and hidden voids from former tunnels and cellars. The 2019–2020 ground movement events near the Mersey Gateway approach highlighted how variable stiffness can lead to differential settlement in blockwork and framed structures. SPT data at 1 m intervals through the fill and into the underlying sandstone let us map these stiffness changes quantitatively. Where N‑values drop below 8 in the upper 5 m, we flag the need for Improvement or deeper founding levels. The test also provides input for liquefaction susceptibility assessment in the saturated sands beneath the waterfront – a requirement under Eurocode 7 for Seismic Design Category 2 structures.

Technical data

Parameter	Typical value
Standard reference	BS EN ISO 22476-3‑18 / BS EN ISO 22476‑3
Hammer energy ratio	60 % (N60 normalised)
Sampler type	Split‑spoon, 35 mm ID / 51 mm OD
Drop height & weight	760 mm / 63.5 kg automatic trip
Typical N‑value range for sandstone	25–60 blows/300 mm
Typical N‑value range for glacial till	12–40 blows/300 mm

Additional services

SPT with Continuous Sampling

Full‑depth SPT profiling from ground surface to rockhead, with split‑spoon samples retrieved for visual classification and moisture content. Suitable for multi‑storey developments, bridge abutments, and retaining walls. N‑values are normalised to N60 and reported with energy efficiency corrections.

SPT for Liquefaction Screening

Dedicated SPT borings in saturated granular soils, with blow counts used in the Youd‑Idriss (2001) methodology to compute cyclic resistance ratio (CRR). Combined with vs30/" data-interlink="1">shear wave velocity measurements from MASW for site class verification under ASCE 7.

Common questions

What is the typical cost of an SPT borehole in Liverpool?

For a single SPT borehole to 10 m depth with sampling every 1.5 m, the cost typically ranges between £370 and £550 depending on access, rig type, and mobilisation distance. Volume discounts apply for multiple boreholes on the same site.

How do Liverpool’s sandstone and glacial till affect N‑values?

The Sherwood Sandstone, when weathered, often gives N‑values of 25–40, while fresh rock can exceed 60. The overlying glacial till, a stiff sandy clay, typically yields N‑values of 12–30. The sharp contrast between these units makes continuous SPT essential to locate the founding stratum accurately.

Can SPT alone confirm liquefaction potential in Merseyside sands?

No. SPT provides the N‑value needed for the NCEER correlation, but we always combine it with grain‑size distribution (fines content) and groundwater monitoring. In Liverpool’s waterfront areas, we run complementary CPTu profiles to capture continuous cone resistance and pore pressure response for a complete liquefaction assessment.

SPT (Standard Penetration Test) in Liverpool – Geotechnical Site Investigation

Process overview

Local context

Need a geotechnical assessment?

Visual overview

Technical data

Additional services

SPT with Continuous Sampling

SPT for Liquefaction Screening

Relevant standards

Common questions

Location and service area